This application is the national phase under 35 U.S.C. xc2xa7371 of prior PCT International Application No. PCT/FI97/00484 which has an International filing date of Aug. 19, 1997 which designated the United States of America.
The present invention concerns a process according to the preamble of claim 1 for the production of 2-butyl-2-ethyl-1,3-propanediol.
According to said process, a reaction mixture is first formed, containing 2-ethylhexanal and formaldehyde, whereafter a suitable hydroxide compound is fed into the reaction mixture, whereby 2-ethylhexanal and formaldehyde react with each other, forming 2-butyl-2-ethyl1,3-propanediol.
The above compound, 2-butyl-2-ethyl-1,3-propanediol, in the following also abbreviated xe2x80x9cBEPDxe2x80x9d, is a substance known per se, which is used for example in the manufacturing of polyester and in the paint industry as a component of powder paints. The excellent UV-protection provided by BEPD, and its very low water adsorption, are some of the advantages of the compound.
BEPD is manufactured from 2-ethylhexanal and formaldehyde in a single-step process through aldol addition, immediately followed by a Cannizzaro reaction. In the first reaction of the process, i.e. the aldol reaction, a basic alkali metal hydroxide or an alkaline earth metal hydroxide is usually used as a catalyst. In the second phase of the process, said hydroxide acts as a reactant, reacting with BEPD-aldol, an intermediate product of the aldol reaction. The hydroxide compound is fed to the reaction mixture in the form of an aqueous solution, whereby a two-phase product mixture is obtained when the reaction is complete. The organic phase of the mixture contains BEPD and the aqueous phase contains alkali metal or alkaline earth metal formates. The product reaction is very exothermic; the released heat of reaction is 200 kJ per mole of BEPD produced.
Known manufacturing processes of BEPD are described e.g. in U.S. Pat. Nos. 5,146,004, 5,177,267 and 5,235,118, in International Patent Application No. WO 93/02035, and in the JP Patent Applications 02062836 and 62129233.
Some considerable draw-backs are connected with the known methods. For example, the yields of BEPD are low, typically below 85%, and the production processes described in the prior art, have mostly been poorly reproducible on the basis of the information supplied in the publications. Low yields are at least partly due to the fact that heavy by-products are formed in the reaction mixture, under the influence of the heat released in the production process. They may amount to upto 20%, and thus significantly decrease the yield of BEPD. On the other hand, the reaction times must be kept quite long, from an economic point of view, because of the violent heat production of the exothermic reaction, which otherwise easily may push the reaction beyond control.
For the sake of completeness, it should be mentioned that there are methods known in the art for preparing which 2,2-disubstituted 1,3-propanediols from the aldehyde by aldol condensation and a subsequent Cannizzaro reaction, in which the alkali is fed into the reaction mixture at two feed rates. Reference is made to the following publications: DE Patent Specification No. 1,057,083, U.S. Pat. No. 2,778,858 and Chemical Abstracts 115 (1991) 255628w. In these technical solutions there is an interval between the feeds and the heat production is also rather uncontrolled.
In our earlier invention, described for example in the International Patent Application No. WO 95//00464, a solution has been disclosed for the production of BEPD using a phase shift catalyst. This process, in which a formaline solution, almost free from methanol, or instead of a solution, solid paraformaldehyde, is used, allows for very good yields (up to over 92%) and low reaction times.
It is an object of the present invention to eliminate the draw-backs of the known technique and to achieve a new process for the production of BEPD with high yield and as pure a product as possible, starting from 2-ethylhexanal and a formaline solution containing methanol, and using an alkali metal or alkaline earth metal hydroxide or similar hydroxide compound as catalyst and reactant.
The present invention is based on the concept of feeding the hydroxide compound continuously and incrementally into the reaction mixture of 2-ethylhexanal and formaldehyde in order to control the heat production of the reaction. Thereby the feeding rate of the hydroxide compound is not constant throughout the reaction, but it is increased stepwise or continuously. Thus, in the beginning of the reaction, when the production of reaction heat is at its highest, the hydroxide compound is fed into the reactor at a rate smaller than that used in the prior art, after which the input is increased as the reaction proceeds.
More specifically, the process according to the invention is mainly characterized by what is stated in the characterizing part of claim 1.
The invention provides considerable advantages. Thus, for instance, the production of BEPD is fully controlled, safe, and gives high yields. Furthermore, the formation of byproducts may be minimized. As shown in the examples below, less than 5% by-products are formed in the conditions according to the invention. The use of the cooling capacity of the production equipment can be made more efficient by the invention. Compared to the above mentioned publications, DE Patent Specification No. 1,057,083, U.S. Pat. No. 2,778,858 and Chemical Abstracts 115 (1991) 255628w, the invention avoids uncontrolled temperature variations and the reaction temperature can be adjusted with an accuracy of one degree even on a production scale basis. Furthermore, by proper control of the thermochemistry it is possible considerably to shorthen the reaction time and no additives are needed for homogenization of the reaction mixture.
In the following, the invention is disclosed through a more detailed description and some working examples.
The production is carried out as a batch, semi-batch or continuous process. The latter two modes are considered the most advantageous. The examples below describe the implementation of the process in a semi-batch reactor equipped with efficient mixing, whereby the calculated amount of 2-ethylhexanal and formaldehyde is first fed into the reactor, forming the reaction mixture, whereafter a suitable hydroxide compound is added to the reaction mixture. Hydroxide is continuously brought into to blend in order to control the heat of reaction. This will also appear from the attached drawing which depicts the generation of reaction heat as a function of the reaction time. The reaction mixture is mixed throughout the reaction. After the reaction, the two-phase reaction mixture is allowed to separate in phases. The organic phase of the mixture contains BEPD, possibly together with some organic impurities. The water phase contains alkali metal or alkaline earth metal salts. The reaction mixture can be separated and washed in two alternative ways, described in more detail below.
The incremental feed of the hydroxide compound can, according to the invention, be accomplished either continuously or in steps. In the latter case, the hydroxide compound is fed at, at least, two different rates, so that the heat production of the reaction between 2-ethylhexanal and formaldehyde, is at least approximately equally large after each increase of feeding rate. The hydroxide compound can be fed into the reaction mixture also at three or more different feeding rates, whereby the new rate is always about 10 to 100%, preferably about 20 to 80%, larger than the previous rate.
In an alternative embodiment, the feed is continuous and the feeding rate of the hydroxide compound is continuously increased. In both embodiments, the amount of hydroxide compound fed into the reaction per unit time is increased at least by a factor of 1.5 or 2 during the reaction.
The amount of hydroxide compound to be fed depends on the amount of 2-ethylhexanal. According to the invention, it has been found preferable to keep the molar ratio of the total input of hydroxide compound (i.e. the total amount of hydroxide fed into the reaction mixture) and 2-ethylhexanal at a value, which is larger than 1, preferably about 1.2 to 1.5.
In the invention, 2-ethylhexanal is preferably used in the form of as pure as possible a solution (purity preferably  greater than 90%, in particular over 95%). Formaldehyde and the hydroxide compound are used in the form of aqueous solutions, preferably as concentrated aqueous solutions, whereby the concentration of formaldehyde in the aqueous solution is 30 to 50 weight-%. This aqueous solution contains most preferably 2 to 20 wt-% some lower alcohol, such as methanol. Methanol or a corresponding alcohol stabilizes the formaline solution and prevents dimerizing of formaldehyde. The hydroxide compound is most preferably used in the form of as strong as possible an aqueous solution or suspension, the concentration of e.g. sodium hydroxide being preferably over 40%, in particular over 45%. In addition to sodium hydroxide, other alkali metal hydroxides may be used as hydroxide compounds, for instance potassium or lithium hydroxide, and alkaline earth metal hydroxides, such as calcium and magnesium hydroxide. The molar ratio of formaldehyde to 2-ethylhexanal is about 2.1 to 5, preferably 2.3 to 3.0, and the corresponding molar ratio with respect to the hydroxide compound is 1.5 to 3, preferably about 1.9 to 2.1.
It should be mentioned, that besides the formaline solution, paraformaldehyde can also be used, which decomposes in the reaction mixture, forming formaldehyde.
The temperature of the reaction is kept at 40 to 80xc2x0 C., preferably 50 to 70xc2x0 C., at least essentially during the reaction. At lower temperatures the reaction phases of the process may constitute a safety risk, because of the reaction kinetics. The reaction time varies depending on the amounts of reactants, on the reaction temperature, and in particular on the amount of hydroxide compound feed, but is typically about 1 to 24 hours, preferably about 4 to 12 hours. In the examples described below, 6 hour reaction times were used. The 2-ethylhexanal used as feedstock reacts usually completely within 4 hours; and t he concentration of the BEPD-aldol that is formed as an intermediate product is at its highest (ca 50%) after about three hours.
After the reaction is completed, the yield of BEPD calculated from ethylhexanal is over 90%. The reaction mixture is removed from the reactor, the blend is washed, and BEPD is separated from the organic phase by distillation at reduced pressure. By washing the BEPD the alkali or earth alkaline salts, formed in the reaction, are principally separated from the product. Heavy organic impurities are removed from BEPD in connection with the distillation.
BEPD may be purified by a method known per se, for instance:
The reaction mixture is first neutralized with (concentrated) sulphuric acid, setting the pH value to 5-7. After this, the reaction mixture is mixed for 1-60 minutes, typically ca 5-30 minutes, after which the phases are allowed to separate, the aqueous phase is removed and the organic phase is washed twice during mixing. The first washing is performed with water containing sodium hydroxide, which increases the pH value to ca 12-14; the second washing is done using acidified water (sulphuric acid), to make the pH value at least about neutral (ca 6 to 7). After each washing turn the phases are allowed to separate and the aqueous phase is removed. The objective of the alkaline washing is to separate the acid fractions, which may disturb the distillation of BEPD and cause problems with corrosion. The raw BEPD product obtained is distilled at low pressure at 120-140xc2x0 C. (9 mmHg). Salts can be recovered from the aqueous phase, separated form the product blend, and further processed.
In an alternative washing method, preferred according to the invention, the reaction mixture is not neutralized with sulphuric acid after the completion of the catalyst feed. Instead, the produced blend is allowed to separate into phases, and the aqueous phase is removed from the reactor as soon as possible after the completion of the catalyst input. After this the produce is washed in the reactor in one or two steps with pure water. The mass of the washing water in relation to the mass of the organic phase is 0.2 to 1.0, preferably 0.4 to 0.5, in the first step, and 0.2 to 1.0, preferably 0.2-0.4 in the second step, if a two-step washing is used. In the case of single-step wash, the corresponding ratio is 0.5 to 0.9. In the purification of the product, a washing efficiency of up to 94 to 96% is attained, including the concentration of the sodium (or corresponding alkali metal or alkaline earth metal) ion. If necessary, the pH value is controlled in connection with the latter washing, as described above. The produced raw BEPD product is distilled as described above.
The washing method disclosed above has some important advantages compared to the traditional method of washing. For instance, the number of processing phases is smaller, because no addition of sulphuric acid is needed. The product phase may be washed with pure water instead of with lye containing water, because no shifting of pH back to the neutral range is needed. The costs of raw material are lower, because no sulphuric acid or lye is needed in connection with the washing. The washing efficiency is better, because the ion content of the product is not increased during the washing. For the same reason, the ionic content of the process and washing waters are lower, leading to less environmental loading. In the distillation of the product, acid fractions can be avoided (meaning less problems with corrosion). If necessary, the washing of the product may be done in one step.
The following non-limiting working examples illustrate the invention.